Design and Molding Simulation of a Plastic Part - EWP

Design and Molding Simulation of a Plastic Part
by
Jiajun Shen
An Engineering Project Submitted to the Graduate
Faculty of Rensselaer Polytechnic Institute
in Partial Fulfillment of the
Requirements for the degree of
MASTER OF ENGINEERING IN MECHANICAL ENGINEERING
Approved:
_________________________________________
Ernesto Gutierrez-Miravete, Engineering Project Adviser
Rensselaer Polytechnic Institute
Hartford, Connecticut
Apr, 2010
CONTENTS
LIST OF SYMBOLS ............................................................................................................... 2 LIST OF TABLES ................................................................................................................... 3 LIST OF FIGURES ................................................................................................................. 4 Abstract .................................................................................................................................... 5 1. Introduction........................................................................................................................ 6 2. Problem Description ........................................................................................................ 10 3. Methodology and Analysis .............................................................................................. 11 3.1 Product Development Environment ....................................................................... 11 3.2 Mold Flow Theoretical Background ...................................................................... 12 3.2.1 Governing Equations.................................................................................. 12 3.2.2 Numerical Method ..................................................................................... 13 3.3 Finite Element Analysis and Details ...................................................................... 13 3.3.1 Pre-processor .............................................................................................. 13 3.3.2 Finite Element Optimization ...................................................................... 13 3.3.3 Single Cavity Mold Design ........................................................................ 16 3.3.4 Material Specification ................................................................................ 17 3.4 Design of Experiments (DOE) ............................................................................... 18 3.4.1 DOE Factors ............................................................................................... 18 3.4.2 Key Factors ................................................................................................ 19 3.5 Multi-cavity Mold Design ...................................................................................... 24 3.6 Additional Results and Discussion ........................................................................ 25 3.7 Another option to reduce warpage ......................................................................... 27 4. Conclusion ....................................................................................................................... 28 5. References........................................................................................................................ 29 1
LIST OF SYMBOLS
∇ =vector operator del, m-1
u=velocity vector, ms-1
ρ =density, kgm-3
t=time, s
p=pressure, kPa
τ =momentum flux tensor, Nm-2. τ xx τ yx τ zx are components of the momentum flux
tensor, where subscripts refer to direction of momentum transfer and direction of
velocity.
S M =body force due to gravity, N. S Mx S My S Mz are components of the body force.
S E =a source of energy per unit volume per unit time, W
Pinlet =fluid inlet pressure, kPa
P0 = fluid initial pressure at gate location, kPa
Tinlet = fluid inlet temperature, °C
T0 =fluid initial temperature at gate location, °C
nwall =normal vector, perpendicular to the surface
Twall =outer surface temperature, °C
Tmold =mold temperature, °C
Pfront =front fluid pressure, kPa
k =thermal conductivity, W m-1 K-1
2
LIST OF TABLES
Table 1 DOE factors ........................................................................................................ 18
Table 2 Parameters used in the analysis .......................................................................... 19
Table 3 Factorial design................................................................................................... 19
Table 4 Single cavity analysis results .............................................................................. 20
3
LIST OF FIGURES
Figure 1 World consumption of plastics by weight ........................................................... 6 Figure 2Main components of the Schick intuition razor ................................................... 7 Figure 3 Razor shaving mechanism diagram..................................................................... 8 Figure 4 Paddle movements – to the right ......................................................................... 8 Figure 5 Paddle movements – to the left ........................................................................... 9 Figure 6 Inner slider drawing .......................................................................................... 10 Figure 7 CAD/FEM data exchange ................................................................................. 11 Figure 8 Tetrahedral elements ......................................................................................... 14 Figure 9 Symmetrical mesh ............................................................................................. 14 Figure 10 Non-symmetrical mesh ................................................................................... 15 Figure 11 Mesh statistics ................................................................................................. 15 Figure 12 Aspect ratio ..................................................................................................... 15 Figure 13 Single cavity mold design ............................................................................... 16 Figure 14 a,b Mechanical properties of Ultraform N2320 .............................................. 17 Figure 15 DOE analysis result ......................................................................................... 20 Figure 16 Warpage under condition A ............................................................................ 21 Figure 17 Actual part under condition A ......................................................................... 21 Figure 18 Warpage under condition B............................................................................. 22 Figure 19 Actual part under condition B ......................................................................... 22 Figure 20 Warpage under condition C............................................................................. 23 Figure 21 Actual part under condition C ......................................................................... 23 Figure 22 Hot runner system ........................................................................................... 24 Figure 23 Multi-cavity mold design ................................................................................ 24 Figure 24 Warpage results for a multi-cavity mold ......................................................... 25 Figure 25 Comparison of length results........................................................................... 26 Figure 26 Comparison of warpage results ....................................................................... 26 Figure 27 Compensation design ...................................................................................... 27 Figure 28 Warpage result of opposite design ................................................................. 27 4
Abstract
The Schick Intuition female all-in-one razor is the first refillable razor for women
designed to make shaving easier. It has gained a significant market share since it was
launched in 2003.The razor was designed with plastic components forming the overall
structure. This was achieved by utilizing Computer Aided Design (CAD) and analysis
models to ensure the success of the design.
In this project a component referred to as “Inner Slider” was chosen for a
comprehensive design review and mold flow analysis. The function of the inner slider is
to translate the movement of the soap in relation to the shaving cartridge. As the soap is
consumed during the shaving process the slider allows the cartridge to remain in contact
with the skin. As an additional requirement, the inner slider must have the ability to pass
a drop test when the entire assembly is dropped to the floor. This study will provide two
proposed design solutions for the inner slider. Each solution can be validated by using
two dimensions as a point of reference to measure deformation.
The design task is to construct the part while concurrently meeting the functional
requirements by using Pro/Engineer software. The mold flow analysis is used to predict
the deformation of the part, and then adjust the design accordingly and this is done using
the Mold-Flow system.
A Design of Experiments (DOE) of the molding process
parameters is used to identify key molding parameters by analyzing a single cavity
injection system. An additional analysis of a multi-cavity system has been performed
and the results compared with those obtained for the single cavity system. Measurements
of an actual part were also collected.
5
1. Introduction
Plastics are widely used in the modern world and it is hard to imagine our life
without them. The first human made plastic was invented by Alexander Parkes in 1855
[1] and since that time plastics have jumped to the No.1 material used, by weight, in the
past century (Figure 1) [2].
Figure 1 World consumption of plastics by weight
Plastics have advantages such as cost, lightweight structure, resilient, resistance to
corrosion, color fastness, transparency, ease of processing, etc. They are being used in a
wide variety of fields such as the medical industry, where they are used for detailed
modeling of organs. In the architectural design industry, plastic forms are used to create
scale replicas of proposed buildings.
The wide range and various types of plastic materials that are available today can be
designed and processed successfully while still meeting high quality, performance, and
profitability requirements. Today and in the future companies must continue to produce
high quality parts in order to remain competitive in the global marketplace. With the
help of computer technology plastic design and processing limitations have been
gradually reduced while the quality has improved significantly.
3D modeling is defined as the process of developing a mathematical representation
of any three dimensional surface of an object. Examples of 3D modeling software that
6
have been widely used for this task include systems such as Pro/Engineer, Uni-graphics,
and SolidWorks. Examples of analytical software include systems such as Ansys,
Comsol, Moldex3D, and Mold-Flow. The design and analytical computer programs,
when utilized together, can help to achieve a high degree of accuracy in manufacturing.
This ultimately leads to dramatically reduced development costs which results in a
shorter time period for delivering a product to the market.
The Schick Intuition female all-in-one razor is the first refillable razor for a woman
that was designed to provide a constant source of lubrication while shaving. This product
was developed in order to meet a need of consumers that was identified during the hair
removal process. It has claimed a significant portion of the market since it was launched
in 2003 (Figure 2).
Figure 2Main components of the Schick intuition razor
The Shaving Cartridge is assembled to the Inner Slider and these components are
then placed within the Outer Slider. The Soap is then fixed to the Outer Slider
completing the sub-assembly. Last, a Paddle component is attached to the exposed slot
on the Outer Slider and the entire assembly is placed within the Handle and secured.
Once this has been completed the Paddle is allowed to rotate on its axis (Figure 3).
When the Paddle rotates it drives the movements of the Inner Slider and Outer
Slider simultaneously. The Sliders now are allowed to transform the movement of the
Soap in a constant relationship to the Shaving Cartridge. If the Cartridge is pushed into
7
the Soap (Figure 4) during use the Soap will now touch the skin first. When the Soap is
consumed during the shave stroke cycle, the Cartridge Blades protrude slightly from the
Soap (Figure 5). As the Blades continue to be in contact with the skin they will be
pushed inward, resulting in the Paddle rotating, to drive the Outer Slider/Soap assembly
forward. This motion will now move the Soap which results in the blade tips and the
Soap to be on the same dimensional plane referred to as a mechanism neutral position
(Figure 3).
Figure 3 Razor shaving mechanism diagram
Figure 4 Paddle movements – to the right
8
Figure 5 Paddle movements – to the left
In order to keep the cost of goods (COG) as low as possible, the molding cycle time
must be as efficient as practical in order to keep high productivity while still maintaining
acceptable quality levels.
9
2. Problem Description
Within the Intuition shaving cartridge, the angle of the blades plays a critical role
during the shaving process. This can be adversely affected even by slight deformation of
the inner slider component. The key task in the design and analysis is how to make the
inner slider as dimensionally accurate as possible.
The shape of the inner slider is determined by the design and is also influenced by
the injection molding process. Post molding deformation could change the shape of the
part completely. The objective of this project is how to optimize the design, while
accounting for the process deformation by analyzing the molding process.
To meet the required movement of the cartridge, while still considering the
manufacturing variance, the inner slider was designed using standard GT&D tolerance
criteria (Figure 6). A critical dimension of the component is the overall inner slider
length (34±0.15mm) and the flatness (0.15mm) of the top surface. The plastic material
that was chosen, in part, due to its mechanical and lubricious characteristics is a
Polyoxymethyene (POM) Ultraform N2320-003.
Figure 6 Inner slider drawing
This study focused on two conditions:
•
The location of the deformation within the part
•
The minimal deformation that can be expected by utilizing various process
conditions during molding.
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3. Methodology and Analysis
3.1 Product Development Environment
The part was designed using the Pro/Engineer software. This is a CAD application,
using feature-based parametrical construction tool modules that support all activities
related to modeling of the plastic part as well as the injection mold. It maintains all
parameters, which is also useful during the injection molding analysis, in order to
identify the parting plane and define cavity layouts.
The mold design is carried out by using both feature-based and parametric
approaches. When the type and structure of the mold are initially defined, the values
associated to the main parameters are given in order to specify the mold geometry. As
the CAD and FEM process are interactive, designers are required to prioritize important
elements within different parts. The data exchange between CAD and FEM is realized in
several steps (Figure 7) [3].
Figure 7 CAD/FEM data exchange
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3.2 Mold Flow Theoretical Background
3.2.1
Governing Equations
The mold filling problem involves the solution of the governing equations for mass,
momentum and energy transport.
The equations governing the flow of incompressible fluid include [4]:
The conservation of mass (continuity)
∇⋅u = 0
The momentum conservation equations in three dimensions
ρ
Du ∂ (− p + τ xx ) ∂τ yx ∂τ zx
+ S Mx x-moment
+
+
=
Dt
∂z
∂x
∂y
ρ
Dν ∂ (− p + τ yy ) ∂τ xy ∂τ zy
=
+
+
+ S My y-moment
Dt
∂y
∂x
∂z
ρ
Dw ∂ (− p + τ zz ) ∂τ xz ∂τ yz
=
+
+
+ S Mz
Dt
∂z
∂x
∂y
(1)
z-moment
And the energy conservation equation
⎡ ∂ (uτ xx ) ∂ (uτ yx ) ∂ (uτ zx ) ∂ (υτ xy ) ∂ (υτ yy ) ⎤
+
+
+
+
⎢
⎥
∂y
∂z
∂x
∂y ⎥
DE ⎢ ∂x
=
+ div(kgradT ) + S E (2)
ρ
⎥
Dt ⎢ ∂ (υτ zy ) ∂ ( wτ xz ) ∂ ( wτ yz ) ∂ ( wτ zz )
+
+
+
⎢+
⎥
∂z
∂x
∂y
∂z
⎣
⎦
The boundary conditions are [5]:
at the injection gate,
Pinlet = P0
(3)
Tinlet = T0
at the mold wall,
∂P
=0
∂nwall
(4)
Twall = Tmold
and on the front flow region,
Pfront = 0
(5)
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3.2.2
Numerical Method
The mold filling process requires solving a non-steady state flow problem involving
a moving free surface, which means that the computation domain changes continuously
with time.
The numerical solution is based on a hybrid finite-element finite-difference method
of solving the pressure, flow and temperature fields, and a control-volume method to
track down the moving flow fronts. In order to solve the governing equations, the
domain is discretized using a collection of tetrahedral finite elements (Figure 8). A
tetrahedral element consists of four sub-volumes divided by four control surfaces. Each
control volume is composed of sub-volumes surrounding a node. The net flux of mass,
momentum, energy through the control surfaces is conserved rigorously within the
corresponding control volume.
Equations (1) and (2) include a generation term which is a function of the
temperature, they are all coupled and must be satisfied simultaneously. The key step of
the numerical method is the integration of the governing equations over a control volume
to yield a discretized equation at its nodes. The resulting system of linear algebraic
equations is solved using the Algebraic Multi Grid (AMG) method.
3.3 Finite Element Analysis and Details
3.3.1
Pre-processor
The pre-processor is used to confirm the integrity of the model in order to achieve
an accurate analysis. It is acceptable to remove small features such as corner blends,
radii from mid-plane and dual models in order to reduce computing time without
significantly affecting the results.
3.3.2
Finite Element Optimization
The use of an optimized 3D mesh for this part is critical in order to achieve accurate
results. A 3D mesh represents the CAD model by filling the volume of the model with
four-node tetrahedral elements (Figure 8). 3D meshes work well for parts that are thick
or solid, since the tetrahedral elements give a true 3D representation of the model. Other
13
examples of meshes are Mid-plane and Dual Domain. These types however, are more
applicable for thin-walled, shell-like parts.
The 3D mesh analysis that is used in this project requires more computational time
to complete. However, this 3D tetrahedral mesh is more appropriate for our thick,
complicated shaped model.
Figure 8 Tetrahedral elements
Due to the part being symmetrical, the correct approach consists in creating a mesh
from one half of the part and then mirrors it (Figure 9). This guarantees that the resulting
complete part is symmetrical. By choosing to mesh the entire part one cannot guarantee
that features within the part are truly symmetrical (Figure 10).
Figure 9 Symmetrical mesh
14
Figure 10 Non-symmetrical mesh
When checking a completed mesh for errors, important mesh statistics must be
closely watched in order to achieve accurate results. The report below (Figure 11) shows
that the selected mesh is of good quality and that it is acceptable for further analysis.
Figure 11 Mesh statistics
The aspect ratio of an element is described as the ratio of the longest side in relation
to the height perpendicular to that side (a/b in Figure 12). While for tetrahedral elements
the max AP allowed by Mold-Flow is 50:1. The maximum used in this study is about 9.
Figure 12 Aspect ratio
15
3.3.3
Single Cavity Mold Design
The purpose of the single cavity analysis is to verify the key factors involve in
plastic part warpage and to provide parts for quality testing, color selection, and samples
for demonstration purposes. The mold should be designed in order to be simple enough
to be fabricated quickly at minimal cost. In this project a cold runner system was used in
order to further reduce these costs (Figure 13).
A cold runner system is an economical process used to produce plastic parts of
simple design. The intent is to reduce the complexity of the tool when compared to a full
hot runner system. It also has the advantage of requiring less skill to set up and operate
as well as providing reduced maintenance costs.
In regards to the type of gating that is required on plastic parts there are many types
that are acceptable. The location of the gate is determined by three main factors
• The gate location should allow molten plastic material to fill the most outward
areas simultaneously.
• The gate should be located on a flat surface when possible. In other instances a
specific feature may be added to the part design in order to incorporate a gate.
• The location should be a result of the whole mold layout considering cooling
system, ejection pin location, and steel thickness.
Figure 13 Single cavity mold design
16
3.3.4
Material Specification
Polyoxymethyene (POM) Ultraform N2320-003 [6] was used in this study. This
molten polymer is non-Newtonian fluid whose flow properties are complex functions of
temperature and shear rate (Figure 14 a, b).
Figure 14 a,b Mechanical properties of Ultraform N2320
17
3.4 Design of Experiments (DOE)
3.4.1
DOE Factors
There are three main contributors to the warpage of a plastic part. One is the
shrinkage of the material due to differential cooling. The second is differential shrinkage
which is due to shrinkage variations between the length and the width of a part. The third
one is orientation. Since this resin is isotropic, there is no orientation shrinkage.
Differential cooling shrinkage is the shrinkage contribution due solely to
temperature gradients within the part. While the part is in the mold, temperature
differences from one side of the mold to the other cause variations in shrinkage through
the thickness of the component.
Differential shrinkage is linear shrinkage given by S = 1 − 1 − S iso which is used
for the fill+pack analysis, where S iso is the isotropic shrinkage of the material, which is
2% from the material data sheet. The part is scaled to
1
1
=
= 1.02 to
1 − S iso 1 − 2%
compensate for the isotropic shrinkage.
Many parameters can be used to control the injection process such as cycle time,
injection pressure, coolant flow rate, mold surface temperature, ejection temperature, etc.
In this study the two key parameters that were chosen to do a Design of Experiments
(DOE) analysis were the cycle time and coolant flow rate (Table 1).
Cycle time is the overall sum of the different process steps of the injection molding
process. It consists mainly of the time required for the part to fill and 80% of the part
thickness to freeze.
cycle time (second) 10 20 30 coolant flow rate (liter/min) 10 15 20 Table 1 DOE factors
18
The values of all the other parameters used in the analysis are given in Table 2.
Mold temperature
Melt temperature
Coolant inlet temperature
Material injection pressure
Injection speed
Filling control
Velocity/pressure switch-over
Tool open/close time
Pack/holding control
90° C
200° C
25° C
70-120MPa
medium-high
automatic
Automatic
5s
80% filling pressure VS time
Table 2 Parameters used in the analysis
3.4.2
Key Factors
There are nine combinations of the selected parameters. The maximum deflection is
the result used to find the relationship between the factors (Table 3). The maximum
deflection is not the dimension that we would like to be measured, but rather the most
easily identified (red colored areas in Figure 16) and we can take advantage of that in
order to identify the relationships between parameters by using the DOE.
A
B
C
D
E
F
G
H
I
Conditions
cycle time
10 seconds
flow rate
10 liter/min
cycle time
20 seconds
flow rate
10 liter/min
cycle time
30 seconds
flow rate
10 liter/min
cycle time
10 seconds
flow rate
20 liter/min
cycle time
20 seconds
flow rate
15 liter/min
cycle time
30 seconds
flow rate
20 liter/min
cycle time
20 seconds
flow rate
20 liter/min
cycle time
30 seconds
flow rate
15 liter/min
cycle time
10 seconds
flow rate
15 liter/min
Max deflection(mm)
Table 3 Factorial design
19
0.4806
0.4734
0.4692
0.4694
0.4735
0.4692
0.4735
0.4694
0.4812
From the factorial DOE analysis (Figure 15), the cycle time was identified as the
most significant contribution to the maximum deflection, whereas the flow rate is not as
important. Therefore the next step was to use a flow rate of 10 liters per minute in order
to get as much productivity as possible and in order to reduce the cycle time as much as
possible.
Figure 15 DOE analysis result
Since the deformation is not very sensitive to the flow rate, a flow rate of 10 liters
per minute was used as a fixed parameter for further analysis. Since the deformation is
very sensitive to the cycle time, the dimension 34±0.15 can meet design requirements
with a cycle time in the range of 10s~30s (Table 4), (Figure 16-21).
Conditions A cycle time: 10s B cycle time:20s C cycle time:30s Max Deflection Dim 1(34±0.15) Dim 2(<=0.15) flow rate: 10L/Min 0.4806 33.95 0.16 0.4734 33.96 0.12 0.4692 33.98 0.10 Table 4 Single cavity analysis results
20
Figure 16 shows the computed warpage obtained by the Mold-Flow software using
a single cavity with a cycle time of 10s, coolant flow rate of 10 liter/min and a cold
runner system; all the other parameters are given in Table 2.
Figure 16 Warpage under condition A
Figure 17 shows the actual warpage obtained in a single cavity mold under the same
conditions as in the previous figure. Although the locations of largest warpage are well
predicted by the software, the actual magnitude in the real part is larger.
Figure 17 Actual part under condition A
21
Figure 18 shows the computed warpage obtained by the Mold-Flow software using
a single cavity with a cycle time of 20s, coolant flow rate of 10 liter/min and a cold
runner system; all the other parameters are given in Table 2. Figure 19 shows the actual
warpage. As seen in the previous case, the overall behavior is well predicted by the code.
Figure 18 Warpage under condition B
Figure 19 Actual part under condition B
22
Figure 20 is the computed warpage obtained by the Mold-Flow software, while
Figure 21 shows the actual warpage using a single cavity with cycle time 30s, coolant
flow rate 10 liter/min, colder runner system, all other parameters are given in Table 2.
The trend observed before still shows here, however, the warpage is slightly smaller as
the cycle time increases.
Figure 20 Warpage under condition C
Figure 21 Actual part under condition C
23
3.5 Multi-cavity Mold Design
The ideal injection molding system delivers molded parts of uniform density and
free from runners, flash, and gate stubs. To achieve this, a hot runner system, in contrast
to a cold runner system, is usually employed (Figure 22). The material in the hot runners
is maintained in a molten state and is not ejected with the molded part. Hot runner
systems are also referred to as hot-manifold systems, or runnerless molding.
Figure 22 Hot runner system
In a production environment the material is delivered within the mold by utilizing
an externally heated runner system that consists of a cartridge-heated manifold with
interior flow passages. The manifold is designed with various insulating features to
separate it from the rest of the mold, thus reducing heat transfer loss. In order to simulate
an actual production mold scenario, the parameters of a mold flow analysis must match
the mold design (Figure 23).
Figure 23 Multi-cavity mold designs
24
Figure 24 is the computed warpage obtained using the Mold-Flow software for 4
cavities with a cycle time 10s, coolant flow rate 10 liter/min, hot runner system; all other
parameters are given in Table 2. The maximum deflection calculated in this case is
0.4967mm. This is a little larger than the computed single cavity deflection of
0.4806mm (Table 4) due to the cold runner system losing heat resulting in a lower fluid
temperature within the cavity when compared to a hot runner system.
Figure 24 Warpage results for a multi-cavity mold
3.6 Additional Results and Discussion
Additional tests were done with fixed flow rate 10 liter/min and with different cycle
times from 10s to 30s at interval of 2s. Both computed warpage by Mold-Flow software
and measurements of actual molding parts were collected and compared (Figure 25, 26).
25
Figure 25 shows measured overall inner slider lengths as well as computed values
for both single-cavity (SC) and multi-cavity (MC) mold. There is a slight increase in
length with cycle time. However, the differences among all these lengths decrease as the
cycle time increases. Also the rate of the decrease is larger for the measured data than for
the predictions.
Figure 25 Comparison of length results
Figure 26 shows flatness data collected from both single-cavity (SC) and multicavity (MC) mold. Computed flatness values are also shown for comparison. The
agreement between measurements and predictions is better for longer cycle time. The
warpage decreases with cycle time. This is more likely due to the longer time spent by
the part inside the mold at long cycle times.
Figure 26 Comparison of warpage results
26
The theoretical analysis produces results that are comparable to measured data,
although a slightly larger. Also, the parts obtained using the hot runner system deviate
more than those from the cold runner system.
Some additional observations include:
•
The analysis does not simulate the ejection. A different ejection pin layout could
change the deflection which can change the residual stress.
•
When the part reaches the ejection temperature, theoretically, this should be the
same as the mold temperature (~90°C). Because the tool temperature varies, and the
inside of the part is like a sandwich, it still retains a considerable amount of heat.
Therefore, it continues to warp even after it is ejected from the tool.
3.7 Another option to reduce warpage
Another way to minimize the warpage is to compensate in the design of the part. If
one designs the deformed area (top surface) with a compensation factor of 0.15mm
(Figure 27). The warpage results show that the top surface is straight which means the
final deflection is zero (0.15mm compensation minus 0.15mm warpage) (Figure 28).
Figure 27 Compensation design
Figure 28 Warpage result of opposite design
27
4. Conclusion
The result of this study using 3D design tools in conjunction with Mold-Flow warp
analysis produced an accurate representation of plastic part deflection.
In summary, the results of this paper have shown the following
• Cycle time is the most critical factor affecting warpage. The longer cycle time,
the less warpage.
• There are three contributors of warpage, the shrinkage due to differential cooling
shrinkage, differential shrinkage and orientation shrinkage. In most cases, the
differential cooling shrinkage and differential shrinkage cannot be avoided.
• A high quality mesh is critical to ensure accurate results.
• A simple DOE is helpful to identify key factors affecting warpage and to
minimize the amount of future work. Experimental evidence collected from
single cavity mold can be used to improve and verify the accuracy of the finite
element solution.
• Compensating the identified areas of potentially high deformation by using
opposite design can also reduce warpage.
Alternately, the study suggested another way of minimizing the deformation by
using a method of compensation in the design. However, if the part is complex, this will
require a substantial amount of time due to features being interactive with one another.
At present, this method has not been tested or verified within our company.
It has been shown in this study that the Mold-Flow analysis can have a significant
positive impact in the design and manufacturing processes. The using of Mold-Flow
could help shorten development time.
28
5. References
[1] Edward Chauncey Worden. Nitrocellulose industry. New York, Van Nostrand, 1911.
[2] Dominick V. Rosato, Donald V. Rosato, Marlene G. Rosato; Plastic Design
Handbook; Kluwer Academic Publishers, Norwell, MA, 2001, p13.
[3] L.M. Galantucci; Evaluation of Filling Conditions of Injection Molding by
Integrating Numerical Simulations and Experimental Tests; Materials Processing
Technology, July 11 2002.
[4] Robert S. Brodkey, Harry C. Hershey; Transport Phenomena; Brodkey Publishing;
Columbus, Ohio, 2001
[5] Seong Taek Lim, Woo II Lee; An Analysis of the Three-dimensional Resin-transfer
Mold Filling Process; Composites Science and Technology; South Korea; Apr 13 1999.
[6] Auto desk Mold-Flow Insight material data warehouse.
[7] E. Alfredo Campo; The Complete Part Design Handbook for Injection Molding of
Thermoplastics; Hanser; Cincinnati, Ohio, 2006.
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